An established non-invasive method for measuring blood flow in the aorta or pulmonary artery is not currently available. We propose to investigate the use of range-gated pulsed Doppler combined with two dimensional echocardiography (Doppler-Echo) for measurement of blood flow in the great arteries. Doppler-Echo measurements of cardiac output obtained in patients during cardiac catheterization or following cardiac surgery will be correlated with simultaneous thermodilution or Fick estimates of cardiac output. Currently available qualitative Doppler-Echo techniques yield much physioloic information. Doppler-Echo technology under development in our laboratory will, we believe, furnish quantitative information about blood flow in the great arteries. Two-dimensional echocardiography (2DE), a complimentary non-invasive method, provides extensive and precise anatomic information in many patients with congenital heart disease. We expect that the combination of Doppler-Echo and 2DE will provide adequate physiologic and anatomic information to allow initial diagnosis and continued follow-up of certain patients with congenital heart disease without the need for cardiac catheterization. We propose to investigate what information is added by cardiac catheterization and angiography following Doppler-Echo and 2DE examination and to evaluate the impact of this information upon patient management. Patients will be stratified for age, size and cardiac lesion to estimate the predictive value of these factors with regard to the reliability of Doppler-Echo and 2DE. Identification of categories of patients in whom cardiac catheterization and aniography add nothing substantive to the Doppler-Echo and 2DE findings could reduce the number of invasive procedures performed and decrease the cost of medical care for many patients with congenital heart disease.